Yu-Hai Yuan

Radio variability properties for radio sources

In this paper, we used the database of the university of Michigan Radio Astronomy Observatory (UMRAO) at three (4.8 GHz, 8.0 GHZ, and 14.5 GHz) radio frequency to analyze the radio light curves by the power spectral analysis method in search of possible periodicity. The analysis results showed that the radio sources display astrophysically meaningful periodicity ranging from 2.2 to 20.8 years in their light curves at the three frequencies. We also calculated the variability parameters and investigated the correlations between the variability parameter and the flux density. For the variability parameters, we found that the parameters at higher frequency are higher than those in the lower frequency. In addition, the variability parameters of BL Lacertae objects are larger than those of flat-spectrum radio quasars. suggesting that they are more variable than flat spectrum radio quasars.

THE SPECTRAL INDEX PROPERTIES OF FERMI BLAZARS

In this paper, a sample of 451 blazars (193 flat spectrum radio quasars (FSRQs), 258 BL Lacertae objects) with corresponding X-ray and Fermi ?-ray data is compiled to investigate the correlation both between the X-ray spectral index and the ?-ray spectral index and between the spectral index and the luminosity, and to compare the spectral indexes ?X, ??, ?X?, and ??X? for different subclasses. We also investigated the correlation between the X-ray and the ?-ray luminosity. The following results have been obtained. (1) Our analysis indicates that an anti-correlation exists between the X-ray and the ?-ray spectral indexes for the whole sample. However, when we considered the subclasses of blazars (FSRQs, the low-peaked BL Lacertae objects (LBLs) and the high-peaked BL Lacertae objects (HBLs)) separately, there is not a clear relationship for each subclass. For the average values, , we have ; and (2) For the correlations between the X-ray and the ?-ray luminosities, we have log ?L ? = (1.033 ? 0.002)log ?L X + (0.213 ? 0.094) for the whole sample, log ?L ? = (0.741 ? 0.004)log ?L X + (12.378 ? 0.162) for HBLs, and log ?L ? = (1.032 ? 0.003)log ?L X + (0.643 ? 0.138) for the LBLs and FSRQs; the correlation slope for HBLs is different from that for FSRQs and LBLs. For the average values, , we have , , and for the X-ray luminosity; and , , and for the ?-ray luminosity. (3) There is an anti-correlation between the effective spectral index, ?X?, and log ?L ? for the whole sample, and the subclasses (FSRQs, LBLs, and HBLs). The effective spectral index shows that (4) For the spectral index difference, ??X?(=?X? ? ??) of the effective spectral index, ?X?, and the ?-ray spectral index, ??, we obtain (5) Based on the Fermi-detected sources, we can say that the HBLs are different from FSRQs, while the LBLs are similar to FSRQs.

The lower limit of the Doppler factor for a Fermi blazar sample

We selected 457 blazars (193 flat spectrum radio quasars, 61 low-synchrotron peaked blazars, 69 intermediate-synchrotron peaked blazars and 134 high-synchrotron peaked blazars) from the second Fermi -LAT catalog (2FGL) of γ-ray sources, which have X-ray observations. We calculated the lower limits for their Doppler factors, δ γ , and compared the lower limits with the available Doppler factors and the apparent superluminal velocities in the literature.

Radio Polarization of BL Lacertae Objects

In this paper, using the database of the university of Michigan Radio Astronomy Observatory (UMRAO) at three (4.8 GHz, 8 GHZ, and 14.5 GHz) radio frequencies, we studied the polarization properties for 47 BL Lacertae objects(38 radio selected BL Lacertae objects, 7 X-ray selected BL Lacertae, and two inter-middle objects (Mkn 421 and Mkn 501), and found that (1) The polarizations at higher radio frequency is higher than those at lower frequency, (2) The variability of polarization at higher radio frequency is higher than those at lower frequency, (3) The polarization is correlated with the radio spectral index, and (4) The polarization is correlated with core-dominance parameter for those objects with known core-dominance parameters suggesting that the relativistic beaming could explain the polarization characteristic of BL Lacs.

Optical Photometrical Observations and Variability for Quasar 4C 29.45

We reported the result of the long-term optical variability of the blazar 4C 29.45s (QSO 1156 + 295, Ton 599), carried out by optical photometric observations in the Johnson V, Cousins RI passbands during 1997 April to 2002 March. We used the 1.56-m telescope of the Shanghai Astronomical Observatory at Sheshan, China, and compiled the post-1974 optical photometric data of the blazar by combining our new observations with the published optical data, and found maximum variations in different passbands: Delta U = 4.41 mag, Delta B = 5.55 mag, Delta V = 4.53mag, Delta R = 5.80mag, and Delta I = 5.34mag. The average color indices are: U - B = -0.54 +/- 0.18 mag, B - V = 0.56 +/- 0.21 mag, B - R = 0.93 +/- 0.18mag, B - I = 1.51 +/- 0.24mag, V - R = 0.44 +/- 0.15mag, and V - I = 1.03 +/- 0.23mag. The post-1974 data give us an excellent opportunity to search for the existence of a possible periodicity in the light curve. In searching for periodicity in the R passband light curve, we performed a Jurkevich test and power spectral (Fourier) analysis methods, as well as CLEANest algorithms to remove false signals. We found possible periods of 3.55 and 1.58 years. A possible mechanism for the periodic variability was analyzed.

The estimations of four basic parameters for gamma-ray loud blazars

The method used in our previous papers is adopted to estimate four basic parameters (the central black hole mass ( M ), the boosting factor (or Doppler factor) ( δ ), the propagation angle ( Φ ) and the distance along the axis to the site of the γ -ray production ( d )) for 59 γ -ray loud blazars (20 BL Lacertae objects and 39 fl at spectrum radio quasars). The central black hole masses estimated for this sample are in a range of from 10 7 M ⊙ to 10 9 M ⊙ In the case of black hole mass, there is no clear difference between BL Lacertae objects and fl at spectrum radio quasars, which is consistent with the previous results suggesting that the central black hole masses do not play an important role in the evolutionary sequence of blazars

Variability and Period Analysis for BL Lac AO 0235+164

Variability is one of the extreme observational properties of BL Lacertae objects. AO 0235+164 is a well studied BL Lac through the whole electro-magnetic wavebands. In the present work, we show its optical R band photometric observations carried out during the period of Nov, 2006 to Dec. 2012 using the Ap6E CCD camera attached to the primary focus of the

A Unification of X-ray selected BL Lacs and FRI Radio Galaxies

\rm 70-cm

Optical monitoring of BL Lac object S5 0716+714 and FSRQ 3C 273 from 2000 to 2014

meniscus telescope at Abastumani Observatory, Georgia. It shows a large variation of

Radio Variability Properties of a Sample of 168 Radio Sources: Periodicity Analysis

\Delta R